1. Field of the Invention
The present invention relates to a brownout protection used for a power supply having a PFC circuit, more particularly, an apparatus of the power supply is provided to inform a microprocessor to process a shutdown procedure when a brownout condition occurs.
2. Description of Related Art
Generally, the power supplies are applied to the power electronic devices. As an abnormal condition occurs on the power supply, the corresponding electronic device, such as the microprocessor on the motherboard, needs to spend a period of time to process the shutdown procedure. When an input voltage of the power supply is lower than a protection voltage, the conventional power supply will be turned off immediately for preventing damage. At present, if the microprocessor can't process the shutdown procedure, the data might be lost.
FIG. 1 shows a schematic circuit of a conventional power supply having a PFC circuit. Following description explains the protection operation of the power supply in case of a brownout condition occurs.
A brownout circuit 220 of a power supply 20 detects an input voltage VIN, such as a rectified input voltage VRECT, and produces a brownout signal SBO when the input voltage VIN is lower than a protection voltage (brownout condition occurs). As a standby circuit 230 receives the brownout signal SBO, it will immediately disable a supply voltage VCC of a PFC circuit 240, a PWM circuit 250 and a supervisor circuit 260. Therefore, an output voltage VOUT of the power supply is cut-off. In the meanwhile, since the supervisor circuit 260 is not powered anymore, it cannot output a power-good signal VPGO to inform the microprocessor to process the shutdown procedure beforehand, such as the procedure of storing data in advance.
Referring to FIG. 2, which shows a timing diagram of the conventional power supply having the PFC circuit in case a brownout condition occurs. As the brownout circuit 220 produces a brownout signal SBO (High Level), the supply voltage VCC of the PWM circuit 250 will be turned off so as to disable a PWM signal SPWM (Low-level) and cut off the output voltage VOUT (Low-level) immediately. Meanwhile, the supervisor circuit 260 cannot output a power-good signal VPGO (Low-level) since its supply voltage is disabled. Therefore, the microprocessor 10 is unable to process the shutdown procedure.
A flowchart of brownout protection method for a conventional power supply having the PFC circuit is shown in FIG. 3. Firstly, the power supply 20 checks the input voltage VIN (P110). As the input voltage VIN is lower than the protection voltage, the brownout circuit 220 will generate the brownout signal SBO to the standby circuit 230 (P120). Finally, the standby circuit 230 will turn off the supply voltage VCC of the PFC circuit 240, the PWM circuit 250 and the supervisor circuit 260 (P130).
As described above, the power supply 20 having the PFC circuit are well known in the market. However, as the brownout condition occurs, the conventional art fails to provide a period of time for the microprocessor 10 to process the shutdown procedure before the microprocessor does not work.